[Clang] Consider outer instantiation scopes for constraint normalization

[zyn0217]

We need to compare constraint expressions when instantiating a friend declaration that is lexically defined within a class template. Since the evaluation is deferred, the expression might refer to untransformed function parameters such that the substitution needs the mapping of instantiation.

These mappings are maintained by the function declaration instantiation, so we need to establish a "transparent" LocalInstantiationScope before substituting into the constraint.

No release note as this fixes a regression in 19.

Fixes #114685

[llvmbot]

@llvm/pr-subscribers-clang

Author: Younan Zhang (zyn0217)

Changes

We need to compare constraint expressions when instantiating a friend declaration that is lexically defined within a class template. Since the evaluation is deferred, the expression might refer to untransformed function parameters such that the substitution needs the mapping of instantiation.

These mappings are maintained by the function declaration instantiation, so we need to establish a "transparent" LocalInstantiationScope before substituting into the constraint.

No release note as this fixes a regression in 19.

Fixes #114685

---

Full diff: https://github.com/llvm/llvm-project/pull/114749.diff

2 Files Affected:

• (modified) clang/lib/Sema/SemaConcept.cpp (+1-1)
• (modified) clang/test/SemaTemplate/concepts-out-of-line-def.cpp (+16)

diff --git a/clang/lib/Sema/SemaConcept.cpp b/clang/lib/Sema/SemaConcept.cpp
index e36ee062213716..bc988001ea7e46 100644
--- a/clang/lib/Sema/SemaConcept.cpp
+++ b/clang/lib/Sema/SemaConcept.cpp
@@ -975,7 +975,7 @@ static const Expr *SubstituteConstraintExpressionWithoutSatisfaction(
   std::optional<LocalInstantiationScope> ScopeForParameters;
   if (const NamedDecl *ND = DeclInfo.getDecl();
       ND && ND->isFunctionOrFunctionTemplate()) {
-    ScopeForParameters.emplace(S);
+    ScopeForParameters.emplace(S, /*CombineWithOuterScope=*/true);
     const FunctionDecl *FD = ND->getAsFunction();
     for (auto *PVD : FD->parameters()) {
       if (!PVD->isParameterPack()) {
diff --git a/clang/test/SemaTemplate/concepts-out-of-line-def.cpp b/clang/test/SemaTemplate/concepts-out-of-line-def.cpp
index fe8f74928fc370..dd518d283c83c8 100644
--- a/clang/test/SemaTemplate/concepts-out-of-line-def.cpp
+++ b/clang/test/SemaTemplate/concepts-out-of-line-def.cpp
@@ -702,3 +702,19 @@ class TTP;
 C v;
 
 } // namespace GH93099
+
+namespace GH114685 {
+
+template <typename T> struct ptr {
+  template <typename U>
+  friend ptr<U> make_item(auto &&args)
+    requires(sizeof(args) > 1);
+};
+
+template <typename U>
+ptr<U> make_item(auto &&args)
+  requires(sizeof(args) > 1) {}
+
+ptr<char> p;
+
+} // namespace GH114685

[zyn0217]

Backport PR #114951

(I have to backport it manually as there are some other changes on the post-19 branch)